 /*******************************************************************************
  * Copyright (c) 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.text.undo;

 import org.eclipse.core.commands.ExecutionException;
 import org.eclipse.core.commands.operations.IUndoContext;

 /**
  * Interface for a document undo manager. Tracks changes in a document and
  * builds a history of text commands that describe the undoable changes to the
  * document.
  * <p>
  * Clients must explicitly connect to the undo manager to express their interest
  * in the undo history. Clients should disconnect from the undo manager when
  * they are no longer interested in tracking the undo history. If there are no
  * clients connected to the undo manager, it will not track the document's
  * changes and will dispose of any history that was previously kept.</p>
  * <p>
  * Clients may also listen to the undo manager for notifications before and
  * after undo or redo events are performed. Clients must connect to the undo
  * manager in addition to registering listeners.</p>
  * <p>
  * Clients may implement this interface.
  * </p>
  *
  * @see DocumentUndoManagerRegistry
  * @see IDocumentUndoListener
  * @see org.eclipse.jface.text.IDocument
  * @since 3.2
  */
 public interface IDocumentUndoManager {

     /**
      * Adds the specified listener to the list of document undo listeners that
      * are notified before and after changes are undone or redone in the
      * document. This method has no effect if the instance being added is
      * already in the list.
      * <p>
      * Notifications will not be received if there are no clients connected to
      * the receiver. Registering a document undo listener does not implicitly
      * connect the listener to the receiver.</p>
      * <p>
      * Document undo listeners must be prepared to receive notifications from a
      * background thread. Any UI access occurring inside the implementation must
      * be properly synchronized using the techniques specified by the client's
      * widget library.</p>
      *
      * @param listener the document undo listener to be added as a listener
      */
     void addDocumentUndoListener(IDocumentUndoListener listener);

     /**
      * Removes the specified listener from the list of document undo listeners.
      * <p>
      * Removing a listener which is not registered has no effect
      * </p>
      *
      * @param listener the document undo listener to be removed
      */
     void removeDocumentUndoListener(IDocumentUndoListener listener);

     /**
      * Returns the undo context registered for this document
      *
      * @return the undo context registered for this document
      */
     IUndoContext getUndoContext();

     /**
      * Closes the currently open text edit and open a new one.
      */
     void commit();

     /**
      * Connects to the undo manager. Used to signify that a client is monitoring
      * the history kept by the undo manager. This message has no effect if the
      * client is already connected.
      *
      * @param client the object connecting to the undo manager
      */
     void connect(Object client);

     /**
      * Disconnects from the undo manager. Used to signify that a client is no
      * longer monitoring the history kept by the undo manager. If all clients
      * have disconnected from the undo manager, the undo history will be
      * deleted.
      *
      * @param client the object disconnecting from the undo manager
      */
     void disconnect(Object client);

     /**
      * Signals the undo manager that all subsequent changes until
      * <code>endCompoundChange</code> is called are to be undone in one piece.
      */
     void beginCompoundChange();

     /**
      * Signals the undo manager that the sequence of changes which started with
      * <code>beginCompoundChange</code> has been finished. All subsequent
      * changes are considered to be individually undo-able.
      */
     void endCompoundChange();

     /**
      * Sets the limit of the undo history to the specified value. The provided
      * limit will supersede any previously set limit.
      *
      * @param undoLimit the length of this undo manager's history
      */
     void setMaximalUndoLevel(int undoLimit);
     
     /**
      * Resets the history of the undo manager. After that call,
      * there aren't any undo-able or redo-able text changes.
      */
     void reset();

     /**
      * Returns whether at least one text change can be rolled back.
      *
      * @return <code>true</code> if at least one text change can be rolled back
      */
     boolean undoable();

     /**
      * Returns whether at least one text change can be repeated. A text change
      * can be repeated only if it was executed and rolled back.
      *
      * @return <code>true</code> if at least on text change can be repeated
      */
     boolean redoable();

     /**
      * Rolls back the most recently executed text change.
      *
      * @throws ExecutionException if an exception occurred during undo
      */
     void undo() throws ExecutionException;

     /**
      * Repeats the most recently rolled back text change.
      *
      * @throws ExecutionException if an exception occurred during redo
      */
     void redo() throws ExecutionException;

     /**
      * Transfers the undo history from the specified document undo manager to
      * this undo manager. This message should only be used when it is known
      * that the content of the document of the original undo manager when the
      * last undo operation was recorded is the same as this undo manager's
      * current document content, since the undo history is based on document
      * indexes. It is the responsibility of the caller
      * to ensure that this call is used correctly.
      *
      * @param manager the document undo manger whose history is to be transferred to the receiver
      */
     public void transferUndoHistory(IDocumentUndoManager manager);

 }

